1. Field of the Invention
The present invention relates to an apparatus and a method for imprinting mask patterns using photolithography on a substrate base for making semiconductor devices, imaging devices (CCD), or liquid crystal display panels and the like, and also relates to a method for adjusting the exposure apparatus. In particular, the present invention relates to technology for exposing a pattern using illumination light such as extreme ultraviolet light (EUV light) such as soft x-rays.
2. Description of the Related Art
When manufacturing semiconductor devices, various apparatuses are used in photolithography for exposing a pattern, fabricated on a mask such as a reticle, on a wafer (or glass plate) as a substrate base. Traditionally, a base is coated with a photo-resist material and is exposed using a projection type apparatus such as a stepper, or a proximity type apparatus for imprinting a pattern directly on the base. In such apparatuses, ultraviolet light such as the i-line of a mercury lamp (365 nm wavelength), or far ultraviolet light (DUV) such as KrF excimer laser light (248 nm wavelength), has been used as illumination light (exposure light). In recent years, exposure apparatuses utilize other light sources, for example, far ultraviolet light such as ArF excimer light (193 nm wavelength) and vacuum ultraviolet light (VUV light) such as F2 laser light (157 nm wavelength), have been developed to produce a higher degree of image resolution. Also, illumination or exposure light systems used for the traditional exposure apparatuses include refraction types and reflection/refraction types.
When using light sources in the ultraviolet region, it is not very efficient to use the exposure light for adjusting the optical systems in the illumination or exposure assembly from the initial primary adjustment stage to the final fine adjustment stage. Therefore, conventionally, a different exposure light, for example, a visible light source such as a Hexe2x80x94Ne laser is used to perform primary adjustments using methods based on collimators or interferometers, and only the final adjustment is performed using the actual exposure light.
As described above, in the conventional methods based on using adjustment light source such as a visible light source, different from the exposure light source, it is necessary to arrange a special optical path for the adjustment light, using devices such as mirrors, so that the light path of visible adjustment beam coincides approximately with the light path of the exposure beam, so that it has been difficult to perform adjustments involving both the exposure light source and the illumination optics. For this reason, it has been difficult to improve the primary or rough adjustment process, resulting in increasing the time required for final or precise adjustment using the exposure light. There has been the drawback that the assembly time is increased. Furthermore, the exposure apparatus requires periodic maintenance of the illumination and exposure optics, but traditionally, the primary adjustment process performed during the periodic maintenance operation has been quite lengthy because of the special arrangement necessary for checking the illumination optics, such as positioning the guide mirrors, thus resulting in a complex and time-consuming operation.
Also, conventional illumination and projection systems are based on a refraction system or a reflective/refraction system, and because the wavelengths for the exposure light and for the visible light are widely separated, the primary adjustment process performed by using visible light for checking resulted in chromatic aberrations in the illumination and projection optics. Chromatic aberrations cause a large error in the rough adjustment results, and contribute to further lengthening the final adjustment task.
Especially, for the future production of even more microscopic semiconductor devices, development work is underway for an apparatus based on an exposure light of less than 100 nm in the extreme ultraviolet range (EUV light). When using EUV light for exposure, because of the large size of the exposure light source, there has been a need for an adjustment method that allows inclusion of the exposure light source for total optical adjustment of the exposure apparatus.
FIG. 14 shows an example of the projection apparatus based on soft x-rays for exposure light. A laser beam in the infrared range or visible range emitted from a laser source 201 is focused by a laser light focusing optics 201a on a focus point 203. An opening of a nozzle 202 is positioned in the vicinity of the focal point 203. A target substance such as a gaseous substance ejected from the nozzle 202 is excited by the high intensity laser light at the focal point 203, and the center portion of the target becomes a plasma, resulting in emission of soft x-ray light. Therefore, the emission point of the x-ray beam is the focal point 203. Simultaneously, infrared light, visible light, and ultraviolet light are generated as well as soft x-rays light.
The soft x-ray beam emitted from the focal point 203 is converted to a parallel beam by the first focusing optic 204 and the second focusing optic 205, and is focused by a condenser optic 207, and after deflecting its optical path by the flat mirror 207a, and is superimposed on a reflective type mask 208. The soft x-ray beam, reflected selectively by the pattern fabricated on the reflective mask 208, is led to the device surface 210 to be exposed by the projection optics 209, thereby imprinting the pattern of the mask 208 on the device surface 210. The portion of the apparatus required for the soft x-rays is located in an evacuated chamber 211 because of the low transmissivity of soft x-rays in air.
In such an apparatus, the nozzle 202 is subjected to some wear because of the plasma generated in its vicinity. Also, the first focusing optic 204 is subjected to contamination from particles worn off the nozzle 202, thus it is thought that the reflection properties may degrade with use. For this reason, it is necessary to replace the parts 202 and 204 periodically. When exchanging these parts, the new parts must be positioned exactly in their original positions. This is because, in the projection exposure technology field, even the slightest deviation in the illumination optical path will cause distortions in the projected image that demands the highest degree of optical precision.
However, because of the immature state of the current projection exposure technology based on soft x-rays as exposure light, there have been no suggestions of methods dealing with the positioning of replacement parts. It is desirable that the devices used in such replacement process should be as economical as possible in view of the fact that the overall projection exposure system is already extremely expensive.
It is an object of the present invention to provide a method for adjusting an exposure apparatus that enables to perform adjustments of internal optics quickly and efficiently.
Also, another object of the present invention is to provide a method for adjusting an exposure apparatus using EUV light for exposure that enables to perform adjustment of internal optics quickly and efficiently.
Further, still another object of the present invention is to provide an exposure apparatus designed for the method invented.
A first method is provided for performing optical adjustments on an exposure apparatus provided with: a light source that generates illumination light for exposure, and illumination optics that irradiates a mask with the illumination light and exposes a mask pattern on a substrate base using the illumination light. The method uses a wide bandwidth light source as the light source that generates an exposure light and a non-exposure light having wavelengths different from the wavelengths in the exposure light; and performs optical adjustments on optical components in at least a part of the illumination optics using the non-exposure light emitted from the wide bandwidth light source.
According to the first method, a portion of the optical components is adjusted using the non-exposure light emitted from the wide bandwidth light source so that optical adjustments can be performed precisely and quickly without relying on a separately provided light source for measuring purposes. Also, the non-exposure light is emitted from almost the same position as the exposure light (approximately coaxially) so that optical components can be adjusted with at the same precision needed for the actual exposure process.
A second method is provided for performing optical adjustments on an exposure apparatus provided with: a light source that generates illumination light for exposure, and illumination optics that radiates a mask with the illumination light and exposing a mask pattern on a substrate base using the illumination light. The method uses a wide bandwidth light source serving as the light source for generating exposure light and non-exposure light having wavelengths different from the wavelengths in the exposure light; performs primary optical adjustments for optical components in at least a part of the illumination optics using the non-exposure light; and performs final optical adjustments for the illumination optics using the exposure light emitted from the wide bandwidth light source.
According to the second method also, rough optical adjustments can be performed quickly and precisely without relying on a separately provided light source for measuring purposes. Therefore, adjustment errors are already minimized so that the final adjustments of the optical systems using the exposure light can be performed quickly.
In these case, it is preferable that the exposure apparatus is provided with projection optics comprised of reflective components for focusing illumination light exiting from a mask so as to imprint a pattern fabricated on the mask on a substrate base, and that adjustments of the optical components in at least a part of the illumination optics and the projection optics are performed using the non-exposure light emitted from the wide bandwidth light source. In the case where the projection optics consists of reflective components, the accuracy of the adjustment using the non-exposure light can be improved because there is no chromatic aberration.
A third method is provided for performing optical adjustments for an exposure apparatus provided with: a light source that generates illumination light for exposure; illumination optics that irradiates a mask with the illumination light; and projection optics that projects a pattern image of the mask on a substrate base. The method uses a wide bandwidth light source for generating illumination light for exposure light and non-exposure light having wavelengths different from the wavelengths in the illumination light; and adjusts at least a part of the projection optics using the non-exposure light. The third method can also perform optical adjustments quickly.
Evaluation methods for adjusting the projection optics may be made by observing a point image or a image space of a periodic pattern on a screen, or a point image may be defocused away from the screen to determine wave-plane aberrations. Any other measurement methods can also be used.
The wide bandwidth light source should generate ultraviolet light as exposure light (wavelengths in a range of 1xcx9c100 nm) and non-exposure light containing at least one of either ultraviolet light (of wavelengths in a range of 100xcx9c400 nm) or visible light (of wavelengths in a range of 400xcx9c800 nm). It is preferable that the illumination optics be comprised by reflective components. Reflective systems do not exhibit chromatic aberration so that the non-exposure light can perform precision optical adjustments. If the non-exposure light is ultraviolet light, simple detectors such as photo-diodes can be used readily, thus resulting in a low cost optical adjustment mechanism. If the non-exposure light is visible, the operator can visually follow the optical paths so that the adjustment process is facilitated.
Also, in the case where the non-exposure light is visible light or ultraviolet light having a wavelength no more than about 200 nm, it is possible to perform optical adjustments in a non-vacuum atmosphere, for example, in air, and the time for the adjustments can thereby be shortened. It is also possible to fill the optical path for non-exposure light with inert gas such as nitrogen or helium, instead of air. In this case, light having a wavelength no more than 200 nm can be used as non-exposure light.
A preferable example of the wide bandwidth light source is a laser plasma light source, and the exposure light is preferably an ultraviolet light of wavelength between 5xcx9c20 nm (EUV light). A laser plasma light source generates light of various wavelengths, by irradiating a target material, such as a copper tape, water drops, ice particles, xenon gas, or krypton gas, with a high power laser beam so that a high temperature plasma is generated. The plasma emits light of various wavelengths when it cools down. The energy of EUV light emitted from a laser plasma light source is deduced to be about 10% of the total energy of light irradiated on the target, and the remainder (about 90%) is emitted as light other than EUV light. In addition, the energy of the light to be used for exposure contained in the EUV light is deduced to be about 1xcx9c2% of the total energy of the light irradiated on the target.
The light other than the exposure light contains light having wavelengths that are very close to that of exposure light, and such light will be absorbed to generate heat by a laminated reflection mirror designed to reflect only a selected wavelength (for example, 13.4xc2x10.1 nm or 11.5xc2x10.1 nm, selected from among 5xcx9c20 nm). In contrast, visible light and ultraviolet light close in wavelength to visible light is reflected by the topmost layer in the laminated reflection mirror which contains substances such as Mo, Be, or Si so as to reach the illumination optics as well as the projection optics. Therefore, if a laser plasma light source is used, exposure light and non-exposure light can be emitted coaxially, and they are preferable for the exposure light source in the present invention.
Also, when optical systems are to be checked using non-exposure light, a gaseous substance (air for example) may be supplied in an optical path of the non-exposure light, and when using exposure light to perform adjustments or exposure, it is preferable to evacuate the optical paths of the exposure light. When the non-exposure light is either visible light or ultraviolet light having wavelengths close to visible light, air and the like supplied to the optical paths does not absorb energy and the adjustment process is facilitated. If the exposure light is EUV light, absorption is high and energy is absorbed if the optical path is not evacuated.
A first exposure apparatus for exposing a mask pattern onto a substrate base is comprised by: a light source that generates illumination light for exposure; and illumination optics that radiates illumination light emitted from the light source on a mask, wherein the light source is a wide bandwidth light source that generates exposure light and non-exposure light having wavelengths different from the wavelengths in the exposure light; and the exposure apparatus is provided with a photo-sensor that detects the non-exposure light that has passed through at least a part of optical components in the illumination optics. The output signals from the photo-sensors are used to enable the first or second method of adjustment of the present invention.
A second exposure apparatus for exposing a mask pattern onto a substrate base is comprised by: a light source that generates illumination light for exposure; and illumination optics that radiates illumination light emitted from the light source on a mask, wherein the light source is a wide bandwidth light source that generates exposure light and non-exposure light having wavelengths different from the wavelengths in the exposure light; and the exposure apparatus is provided with a photo-sensor that detects the non-exposure light that has passed through at least a part of optical components in the projection optics. This apparatus also enables the first or second method of adjustment of the present invention.
In these cases, it is preferable to provide a projection optics for projecting a mask pattern onto a substrate base by focusing the illumination light reflected by the mask. Furthermore, it is preferable that illumination optics and projection optics are comprised by reflective systems, and include stage devices for moving a mask and a substrate base in a given direction; and a control device for scanning the mask and the substrate base concurrently with respect to projection optics, so as to imprint a mask pattern on the substrate base. When the projection optics is reflective, chromatic aberration is eliminated and a good focusing area is formed in an arc shape. A step-and-scan method can then be used to perform exposure over a wide shot area on the substrate base.
Also, it is preferable to provide a wavelength selection device for transmitting one of either exposure light or non-exposure light emitted from the wide bandwidth light source towards the illumination optics side.
Further, if exposure light emitted from the wide bandwidth light source is EUV light, other emitted light having a wavelength longer than EUV light, for example 100xcx9c300 nm, may be used to exposure rough layers or middle layers requiring less precision, so that the EUV light may be used to expose critical layers requiring a higher precision. This procedure allows the present apparatus to be used for a variety of applications.
According to the present method of performing optical adjustments of the exposure apparatus, a light source should generate exposure light as well as non-exposure light so that quick and precise adjustment can be provided for the internal optical components without relying on a separately provided light source for adjustment purposes.
When exposure light is extreme ultraviolet light (EUV) and the illumination optics are reflective, and if the projection optics provided are also reflective, because chromatic aberration is not produced, the use of the non-exposure light can provide quick and precise optical adjustments of the internal optical components.
Also, the present exposure apparatus enables use of the present method of optical adjustments.
On the other hand, another purpose of the present invention is to present a technique using a low cost device for positioning optical components near x-ray generating devices in an exposure apparatus using x-rays as exposure light.
In this case, soft x-rays used as exposure light may be chosen from two kinds of x-rays. One type is emission light from a synchrotron and the other is plasma x-rays, especially those emitted from a plasma excited by laser irradiation.
Emission light from a synchrotron has known problems, such as the expense of the light source, bulky equipment, and because a single source produces x-rays used for several exposure apparatuses, if a problem develops in the single source, all the exposure apparatuses stop operating. Therefore, plasma x-ray devices are regarded as the most suitable type of light source. Therefore, the present invention relies on plasma x-rays.
In order to position newly installed devices in the correct position with respect to the emission point, it is necessary to maintain the relative position of the light source (emission point) with respect to the optical systems. To enable such a process, it is essential to measure where the emission point is. However, optical equipment based on x-rays, all parts of the equipment including the optical paths and the detector devices, tends to be expensive because of its unusual wavelength. Therefore, the present invention focuses attention on the type of light source most suitable for the purpose.
A light source for generating plasma x-rays operates by focusing light energy on a particular point to generate x-rays, therefore, visible light is produced from the same point as the x-rays. Therefore, by observing the emission point of visible light, the emission point for x-rays can be determined. In order to determine the relative position between the light source and the optics, it is sufficient to observe the position of the light source through the optics.
The present invention is achieved based on the above point of view. That is, the exposure apparatus of the present invention comprises an x-ray source that generates x-rays by generating a plasma from a substance so as to use x-rays generated from the x-ray source as exposure light, a light source position observation system is provided to form an image of the x-ray source using light other than x-rays, for example visible light, generated concurrently with the x-rays from the x-ray source.
Another method of the present invention for adjusting an exposure apparatus is a method for positioning an x-ray source for emitting exposure light, comprised by the steps of: generating x-rays from an x-ray source that produces x-rays by generating a plasma of a substance; and positioning the x-ray source using light other than x-rays, for example visible light, generated concurrently with the x-rays.
Another exposure method according to the present invention is a method which uses an x-ray source which generates x-rays by generating of a plasma of a target substance and uses the x-ray as exposure light; and the method adjusts the position of the x-ray source using light other than the x-rays, such as visible light, generated by the x-ray source concurrently with the x-rays; and then performing an exposure process.
According to each of the methods presented above, in an exposure apparatus using x-rays, especially laser plasma x-rays, as a light source for exposure, it is possible to provide high precision in replacing optical components relating to the light source, and furthermore, those parts that are required to realize the present invention have low cost.
Also, the present invention is not limited only to switching of components, and can be also applied to the reposition of optical components in exactly the position required, for example, when they shift their position with use.